The overall goal of this application is to fully characterize the basic biochemical mechanisms which account for the unilateral, permeability form of pulmonary edema which occurs in re- expanded lungs. Re-expansion pulmonary edema (RPE) has traditionally been attributed to forces during expansion which decrease lung interstitial pressure and lead to transudation of fluid. Our preliminary data support the hypothesis that the mechanism of RPE involves oxygen free radical-mediated injury to alveolar-capillary lining cells during rapid re-expansion and re-oxygenation of previously collapsed and hypoperfused lungs. In order to clarify this mechanism, we plan to accomplish the following specific aims: 1) assessment of the pro-inflammatory role of 02 metabolites (including superoxide and H2O2) in RPE, 2) study enzymatic and mitochondrial sources of O2 metabolites along with intracellular antioxidants, 3) investigate the contribution of neutrophils to the unilateral lung injury, and 4) isolate and characterize neutrophil chemoattractants produced during collapse/re-expansion. These experiments will be accomplished using a rabbit model of re-expansion edema in which the effects of free radical probes can be tested. Intracellular antioxidant defenses, especially mitochondrial SOD, will be assessed before and after re-expansion. The effects of extracellular superoxide dismutase (SOD) and catalase (CAT) on edema formation will be tested by intravenous enzyme pretreatment, and liposome-encapsulated SOD and CAT will be used to test the effects of augmented intracellular antioxidant enzymes on edema formation. Additional experiments will be conducted to determine whether aldehyde oxidase is an important source of superoxide or H2O2 in this model. Cyanide- insensitive tissue respiration will be measured as an index of lung free radical formation. Lung lavage fluid will be assayed for chemotactic activity and its cellular composition characterized at various time points before and after re-expansion. The degree of cytotoxic O2 metabolite production, effects of antioxidants, and generation of chemoattractants will also be measured in re- expanded lungs of neutropenic rabbits, to further specify the contribution of neutrophils. This form of unilateral lung injury resembles, in many ways, adult respiratory distress syndrome. It will serve as a model for testing experimental interventions in acute lung injury, since the internal control lung will greatly minimize consumption of experimental animals and no exogenous toxicant need be administered.